(a) Field of the Invention
The present invention relates to a TFT array panel, and in particular, to a TFT array panel for an organic electro-luminescence display.
(b) Description of the Related Art
Generally, an organic electro-luminescence (EL) display is a self emissive display device, which displays images by exciting an emissive organic material to emit light. The EL display includes an anode (hole injection electrode), a cathode (electron injection electrode), and an organic light emission layer interposed therebetween. When charge carriers are injected into the light emission layer, the electrons and the holes are pair annihilated with emitting light. The EL display further includes an electron transport layer (ETL) and a hole transport layer (HTL) for enhancing the light emission of the light emission layer as well as an electron injecting layer (EIL) and a hole injecting layer (HIL).
A plurality of pixels of the EL display are arranged in a matrix and driven in simple matrix type or active matrix type with thin film transistors (TFTs).
The passive matrix type arranges a plurality of anode lines and a plurality of cathode line to intersect each other such that selected one of the anode lines and the one of the cathode lines form a pixel to be driven, while the active matrix type connects TFTs and a capacitor to an anode electrode of each pixel such that the capacitance of the capacitor maintains the voltage of the pixel. A current of a driving TFT for supplying currents to the pixel is controlled by a data voltage supplied through a switching transistor, and a gate and a source of the switching transistor are connected to a gate line (or a scanning line) and a data line intersecting each other. When the switching transistor is turned on by the signal from the gate line, a driving voltage from the data line is applied to the gate of the driving TFT through the switching transistor and the driving TFT supplies a current to the pixels to emit light. The pixels emit red, green and blue lights for color display.
The EL display severely requires uniformity in device characteristics of the driving TFTs. It is because the difference in the device characteristics of the driving TFTs results in different luminance for the same image data and thus it causes non-uniform luminance of a display screen.
A most widely used driving TFT for the EL display includes polysilicon channel layer called low temperature polysilicon (LTPS), which is typically formed by eximer laser annealing (ELA) for crystallizing amorphous silicon. However, the polysilicon formed by ELA may have uneven crystallization due to the deviation in ELA energy, which results in non-uniform device characteristics of the TFTs to deteriorate display characteristics of the EL display.